Method of migrating stored data and system thereof

ABSTRACT

There is provided a storage system and a method of migrating a source data portion from a source logical volume to a destination range in a destination logical volume. The method comprises: configuring a source mapping data structure to comprise an entry associated with said source data portion and indicative of mapping between logical addresses corresponding to said source data portion and addresses corresponding to said source data portion and related to a physical address space; and, responsive to a migration command, configuring a destination mapping data structure to comprise an entry associated with said at least one destination range and comprising a reference to said entry in the source mapping data structure, said entry in the source mapping data structure to be used for mapping to said addresses related to said physical address space and corresponding to the source data portion and to the migrated data portion.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from U.S. Provisional Patent Application No. 61/513,811 filed on Aug. 1, 2011 and is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The presently disclosed subject matter relates, in general, to data storage systems and respective methods for data storage, and, more particularly, to migrating data in the storage system.

BACKGROUND

Minimizing the impact of data migrations on business operations is a critical part of storage management. Technology refresh requiring replacement of older servers or storage arrays with new ones is the major driver of physical data migration. Additionally or alternatively, either because of overall optimization considerations (e.g. CPU usage, memory availability, bandwidth, etc.) or because of configuration modifications (e.g. related to changes in user's privileges, etc.), a decision may come to migrate an application, thus requiring migrating data from one logical volume to another. Wide implementation of Virtual Machines and cloud technologies increases the need for data migration between logical volumes.

The problems of migrating data in the storage systems have been recognized in the conventional art and various systems have been developed to provide a solution, for example:

US Patent Application No. 2011/066597 (Mashtizadeh et al.) discloses a method of migration persistent data of virtual machines. The method includes the steps of copying the persistent data at the source data store to the destination data store, updating a bitmap data structure during the copying step to indicate which blocks of the persistent data have been modified during the copying step, identifying the blocks that have been modified during the copying step using the bitmap data structure, and copying the identified blocks to the destination data store.

US Patent Application No. 2010/299666 (Agbaria et al.) discloses a method for migrating a virtual machine (VM) in a computing environment. The method comprises receiving a request to migrate a VM executing on a source host to a destination host; defining a recovery point to which the VM is restored during recovery from a fault; and iteratively copying a memory of the source host associated with the VM to the destination host. During the copying, the original state of each page in the memory is preserved. At some point, the VM suspends executing on the source host, copies state information associated with the VM to the destination host, and resumes executing on the destination host. If a fault is detected on the source host, the VM is restored to the recovery point using preserved information.

US Patent Application No. 2007/192765 (Shimogawa et al.) discloses a virtual machine system managed by a current host OS virtually operating on hardware. A spare host OS is activated by copying the current host OS to a prescribed memory device using a live migration function when the current host OS is activated, notifies the spare host OS of a request issued to the current host OS via a virtual machine monitor, changes a state of the spare host OS, and switches an OS for managing the virtual machine system from the current host OS to the spare host OS, when the current host OS is in an erroneous state.

US Patent Application No. 2009/125904 (Nelson) discloses migration of a source virtual machine (VM) hosted on a source server to a destination VM on a destination server without first powering down the source VM. After optional pre-copying of the source VM's memory to the destination VM, the source VM is suspended and its non-memory state is transferred to the destination VM; the destination VM is then resumed from the transferred state. The source VM memory is either paged in to the destination VM on demand, or is transferred asynchronously by pre-copying and write-protecting the source VM memory, and then later transferring only the modified pages after the destination VM is resumed. The source and destination servers preferably share common storage, in which the source VM's virtual disk is stored; this avoids the need to transfer the virtual disk contents. Network connectivity is preferably also made transparent to the user by arranging the servers on a common subnet, with virtual network connection addresses generated from a common name space of physical addresses.

US Patent Application No. 2007/220121 (Suwarna) discloses a virtual machine migrated between two servers. A method, at the first server, dismounts a volume on which all the files relating to the virtual machine are stored, and which was previously mounted at the first server. The method, at the second server, mounts the volume on which all the files relating to the virtual machine are stored, so that the second server can host the virtual machine. In this way, the virtual machine can be migrated without having to copy all the files from the first server to the second server. The files relating to the virtual machine are stored on a storage-area network (SAN).

US Patent Application No. 2005/283564 (LeCrone et al.) discloses a method and apparatus for migrating one or more data sets each having one or more extents from one or more source logical devices to one or more target logical devices concurrently with interaction between the application and the data being migrated. A background operation copies each extent from the source logical device to the target logical device in a copy state. When a certain level of data has been copied, the extent is locked to assure synchronization of the data in the target logical device to the corresponding data in the source logical device. The status is changed to a mirrored state. When the extents for a data set in a source logical device or in a group of data sets have been mirrored, all the extents are changed to a diverted state. I/O requests to the diverted extents thereafter are intercepted and processed according to whether they access an extent that is in the copy, mirrored, or diverted state.

U.S. Pat. No. 6,145,066 (Atkin) discloses a computer system including a transparent data migration facility (TDNff) to accomplish automated movement of data (migration) from one location to another in the system. A data migration program includes a main module to control the start of a migration session when said application programs are using data accessed to and from the source volume, to migrate data from the source volume to the target volume, and to end the migration session whereby the application programs are using data accessed to and from the target volume. The data migration program includes a volume module to control the volumes during the migration session. The data migration program includes a copy module to control the copying of data from the source module to the target module during the migration session. The data migration program includes a monitor module for monitoring I/O transfers to the data volumes during the migration sessions. The computer system may have a plurality of operating systems associated with instances of the data migration program which allows for concurrent data migrations. The plurality of instances of the data migration program may also be controlled in a master slave relationship. A migration session may include a plurality of migration phases such as activation, copy, refresh, synchronize, redirect, resume and termination phases.

SUMMARY

In accordance with certain aspects of the presently disclosed subject matter, there is provided a method of migrating at least one source data portion from a source logical volume Vsrc to at least one destination range in at least one destination logical volume Vdest thereby giving rise to at least one migrated data portion in said at least one destination logical volume Vdest. The method comprises:

configuring a source mapping data structure DSsrc to comprise at least one entry associated with said at least one source data portion and indicative of mapping between one or more contiguous ranges of addresses corresponding to said at least one source data portion in the source logical volume Vsrc and one or more ranges of addresses corresponding to said at least one source data portion and related to a physical address space; and,

responsive to a migration command, configuring a destination mapping data structure DSdest to comprise at least one entry associated with said at least one destination range and comprising a reference to said at least one entry in the source mapping data structure DSsrc, said at least one entry in the source mapping data structure DSsrc to be used for mapping to addresses related to physical address space and corresponding to the source data portion and to the migrated data portion.

The method can further comprise addressing a request related to said migrated data portion received by said destination mapping data structure DSdest to said at least one entry in the source mapping data structure DSsrc.

In accordance with further aspects of the presently disclosed subject matter, the destination mapping structure DSdest can be configured as a destination ordered mapping tree TRdest, wherein said at least one entry in the destination mapping structure DSdest is implemented as a leaf of said destination mapping tree TRdest, said leaf bearing, upon receiving the migration command, a reference to said at least one entry associated with said source data portion in the source mapping structure DSsrc.

In accordance with further aspects of the presently disclosed subject matter, the method can further comprise associating said at least one source data portion with a multiple-reference indication indicative of a number of migrated data portions in one or more destination volumes, said migrated data portions mapped to the addresses related to physical address space with the help of said at least one entry associated with the source data portion in the source mapping data structure. The indication can be provided with the help of a reference counter associated with the source mapping data structure DSsrc and with the destination mapping structure DSdest.

The source mapping structure DSsrc can be further configured as a source ordered mapping tree TRsrc, wherein said at least one entry in the source mapping structure DSsrc is implemented as a leaf of the tree TRsrc. The method can further comprise associating said leaves in the source and the destination mapping trees with a multiple-reference indication indicative of a number of migrated data portions in one or more destination volumes, said portions mapped to the addresses related to physical address space with the help of said leaves.

In accordance with further aspects of the presently disclosed subject matter, the method can further comprise: responsive to a write request related to said at least one source data portion, providing an atomic operation, said atomic operation comprising:

assigning a new range of addresses related to physical address space for new data to be destaged;

updating said at least one entry in the source mapping structure DSsrc to map between one or more contiguous ranges of addresses corresponding to said at least one source data portion in the source logical volume Vsrc and said new range of addresses related to physical address space; and

updating said at least one entry in the destination mapping structure DSdest to map between said at least one destination address range and addresses related to physical address space and referred to, before updating, via said at least one entry in the source data structure DSsrc, wherein, upon updating, said mapping is provided without referencing to the source mapping structure.

In accordance with further aspects of the presently disclosed subject matter, the method can further comprise: responsive to a request to delete said at least one source data portion, providing an atomic operation, said atomic operation comprising:

deleting said at least one entry in the source mapping structure DSsrc;

updating said at least one entry in the destination mapping structure DSdest to map between said at least one destination address range and addresses related to physical address space and referred to, before updating, via said at least one entry in the source data structure DSsrc, wherein, upon updating, said mapping is provided without referencing to the source mapping structure; and

updating the value of multiple-reference indication associated with said at least one migrated data portion.

In accordance with further aspects of the presently disclosed subject matter, the method can further comprise: responsive to a write request related to said at least one migrated data portion, providing an atomic operation, said atomic operation comprising:

assigning a new range of addresses related to physical address space for new data to be destaged;

updating said at least one entry in the destination mapping structure DSdest to map between said at least one destination address range and said new addresses related to physical address space and corresponding to the migrated data portion, wherein said mapping is provided without referencing to the source mapping structure; and

reducing by one the value of multiple-reference indication associated with said at least one source data portion.

In accordance with other aspects of the presently disclosed subject matter, there is provided a storage system comprising a plurality of physical storage devices constituting a physical storage space and controlled by a plurality of storage control devices constituting a storage control layer, wherein the storage control layer is operable to enable migrating at least one source data portion from a source logical volume Vsrc to at least one destination range in at least one destination logical volume Vdest thereby giving rise to at least one migrated data portion in said at least one destination logical volume Vdest. The storage control layer further comprises: a source mapping data structure DSsrc configured to comprise at least one entry associated with said at least one source data portion and indicative of mapping between one or more contiguous ranges of addresses corresponding to said at least one source data portion in the source logical volume Vsrc and one or more ranges of addresses corresponding to said at least one source data portion and related to a physical address space; and a destination mapping data structure DSdest configured to comprise at least one entry associated with said at least one destination range and indicative of mapping between said at least one destination range and one or more ranges of corresponding addresses related to the physical address space;

wherein said storage control layer is further operable to configure, responsive to a migration command, said at least one entry in the destination mapping data structure DSdest to comprise a reference to said at least one entry in the source mapping data structure DSsrc, said at least one entry in the source mapping data structure DSsrc is configured to be used for mapping to the addresses related to physical address space and corresponding to the migrated data portion.

In accordance with further aspects of the presently disclosed subject matter, the system can further comprise a plurality of virtual machines, wherein the logical volumes Vsrc and Vdest are associated with different virtual machines.

In accordance with further aspects of the presently disclosed subject matter, the storage control layer can be further configured to provide associating said at least one source data portion and said at least one migrated data portion with a multiple-reference indication indicative of a number of migrated data portions in one or more destination volumes, said migrated data portions mapped to the addresses related to physical address space with the help of said at least one entry associated with the source data portion in the source mapping data structure.

In accordance with further aspects of the presently disclosed subject matter, the source and/or the destination mapping structures can be configured as ordered mapping trees with the leaves associated with a multiple-reference indication indicative of a number of migrated data portions in one or more destination volumes, said portions mapped to the addresses related to physical address space with the help of said leaves.

Among advantage of certain embodiments of the presently disclosed subject matter is the ability of migrating data from a logical volume to another logical volume (e.g. related to different filesystems and/or different Virtual Machines), whilst eliminating a need of using host resources as well as eliminating a need of physically copying data from one location to the other, thereby reducing consumption of host and storage resources including the cache and internal bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the disclosed subject matter and to see how it can be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

FIG. 1 illustrates a schematic functional block diagram of an exemplary storage arrangement in accordance with certain embodiments of the presently disclosed subject matter;

FIG. 2 illustrates a schematic functional block diagram of a control layer configured in accordance with certain embodiments of the presently disclosed subject matter;

FIG. 3 schematically illustrates a non-limiting example of a mapping tree;

FIG. 4 illustrates a generalized flow diagram of a migration process in accordance with certain embodiments of the presently disclosed subject matter;

FIG. 5 schematically illustrates an exemplary mapping of addresses related to source and destination logical volumes into addresses related to physical storage space in accordance with certain embodiments of presently disclosed subject matter;

FIG. 6 illustrates a generalized flow diagram of handling write requests addressed to the migrated address range in the source volume in accordance with certain embodiments of presently disclosed subject matter; and

FIGS. 7 a-7 c schematically illustrate the process of write requests handling detailed with reference to FIG. 6.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the presently disclosed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the presently disclosed subject matter.

Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing”, “computing”, “calculating”, “determining”, “generating”, “writing”, “selecting”, “allocating”, “storing”, “managing” or the like, refer to the action and/or processes of a computer that manipulate and/or transform data into other data, said data represented as physical, such as electronic, quantities and/or said data representing the physical objects. The term “computer” should be expansively construed to cover any kind of electronic system with data processing capabilities, including, by way of non-limiting example, storage system and parts thereof disclosed in the present applications.

The operations in accordance with the teachings herein may be performed by a computer specially constructed for the desired purposes or by a general-purpose computer specially configured for the desired purpose by a computer program stored in a computer readable storage medium.

Embodiments of the presently disclosed subject matter are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the presently disclosed subject matter as described herein.

The references cited in the background teach many principles of migrating data in storage systems that are applicable to the presently disclosed subject matter. Therefore the full contents of these publications are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.

In the drawings and descriptions, identical reference numerals indicate those components that are common to different embodiments or configurations.

Bearing this in mind, attention is drawn to FIG. 1 illustrating an exemplary storage environment in accordance with certain embodiments of the presently disclosed subject matter.

The computer system comprises a plurality of host computers (workstations, application servers, etc.) illustrated as 101-1-101-n sharing common storage means provided by one or more virtualized storage systems. The illustrated storage system 102 comprises a storage control layer 103 comprising one or more appropriate storage control devices operatively coupled to the plurality of host computers and a plurality of data storage devices 104-1-104-n constituting a physical storage space optionally distributed over one or more storage nodes. The storage control layer 103 is operable to control interface operations (including I/O operations) between host computers and the plurality of storage devices. The storage control layer is further operable to handle a virtual representation of physical storage space and to facilitate necessary mapping between the physical storage space and its virtual representation. The virtualization functions can be provided in hardware, software, firmware or any suitable combination thereof. Optionally, the functions of the control layer can be fully or partly integrated with one or more host computers and/or storage devices and/or with one or more communication devices enabling communication between the hosts and the storage devices. Optionally, a format of logical representation provided by the control layer may differ, depending on interfacing applications.

The physical storage space can comprise any appropriate permanent storage medium and include, by way of non-limiting example, one or more disk drives and/or one or more disk units (DUs). The physical storage space comprises a plurality of data blocks, each data block can be characterized by a pair (DD_(id), DBA), and where DD_(id) is a serial number associated with the disk drive accommodating the data block, and DBA is a logical block number within the respective disk. By way of non-limiting example, DD_(id) can represent a serial number internally assigned to the disk drive by the system or, alternatively, a WWN or universal serial number assigned to the disk drive by a vendor. The storage control layer and the storage devices can communicate with the host computers and within the storage system in accordance with any appropriate storage protocol.

Stored data can be logically represented to a client (e.g. a user, an application, etc.) in terms of logical storage devices referred to hereinafter also as logical units, logical volumes or volumes. A logical unit (LU) is a virtual entity logically presented to a client as a single virtual storage device. The logical volume represents a plurality of data blocks characterized by successive Logical Block Addresses (LBA) ranging from 0 to a number LUK. Different LUs can comprise different numbers of data blocks, while the data blocks are typically of equal size (e.g. 512 bytes). Blocks with successive LBAs can be grouped into portions that act as basic units for data handling and organization within the system. Thus, for instance, whenever space has to be allocated on a disk or on a memory component in order to store data, this allocation can be done in terms of data portions also referred to hereinafter as “allocation units”. Data portions are typically of equal size throughout the system (by way of non-limiting example, the size of a data portion can be 64 Kbytes).

When receiving a write request from a host, the storage control layer defines a physical location(s) for writing the respective data (e.g. a location designated in accordance with an allocation scheme, preconfigured rules and policies and/or location available for a log-structured storage, etc.) and further processes the request accordingly. When receiving a read request from the host, the storage control layer obtains the physical location(s) of the desired data and further processes the request accordingly.

Mapping between logical and physical locations of data portions and/or groups thereof is further detailed with reference to FIGS. 2-7. Addresses related to logical locations can be mapped into addresses related to the physical locations with the help of the allocation module 105 operable to provide necessary address translation. The allocation module can be implemented as a centralized module operatively connected to the plurality of storage control devices or can be, at least partly, distributed over a part or all storage control devices.

Logical objects (e.g. data files, multimedia files, database tables, filesystems, etc.) stored in a logical volume V_(src) can be migrated to logical volume V_(dest). The migration may be useful in scenarios involving duplication of virtual hosts or of applications running in a virtual machine environment. In such cases, migration of whole or part of logical volumes may be necessary. Additional scenarios may involve duplicating data for databases backup, filesystem backup, large file cloning, etc.

Optionally, each host can comprise a plurality of virtual machines (not shown). An application from a first virtual machine VM1 running in a host H_(j) can be migrated to a second virtual machine VM2 running in a host H_(k). In this case H_(j) and H_(k) could be the same host. Files (or other logical objects) related to the application, currently stored in an associated volume V_(src) and owned by a file system FS1 associated with VM1 will be migrated to a file system FS2 associated with VM2 and to be stored in volume V2.

The presently disclosed subject matter is not bound by the specific architecture illustrated with reference to FIG. 1, equivalent and/or modified functionality can be consolidated or divided in another manner and can be implemented in any appropriate combination of software, firmware and hardware. The control layer and/or parts thereof can be implemented as suitably programmed computer(s).

Referring to FIG. 2, there is illustrated a schematic functional diagram of the control layer configured in accordance with certain embodiments of the presently disclosed subject matter. The illustrated configuration is further detailed in U.S. application Ser. No. 12/897,119 filed Oct. 4, 2010, assigned to the assignee of the present application and incorporated herein by reference in its entirety.

The virtual presentation of the entire physical storage space can be provided through creation and management of one or more virtualization layers. By way of non-limiting example, the illustrated control layer comprises two interconnected virtualization layers: a first virtual layer 204 operable to represent logical units available to clients (workstations, applications servers, etc.) and characterized by a Virtual Unit Space (VUS); and a second virtual layer 205 interfacing with the physical storage space via a physical storage interface 203. The logical units are represented in VUS as virtual data blocks characterized by virtual unit addresses (VUAs). The second virtual layer 205 is operable to represent the physical storage space available to the clients and is characterized by a Virtual Disk Space (VDS). By way of non-limiting example, storage space available for clients can be calculated as the entire physical storage space less reserved parity space and less spare storage space. The virtual data blocks are represented in VDS with the help of virtual disk addresses (VDAs). Virtual disk addresses are substantially statically mapped into addresses in the physical storage space. This mapping can be changed responsive to modifications of physical configuration of the storage system (e.g. because of disk failure or disk addition). The VDS can be further configured as a concatenation of representations (illustrated as 210-213) of RAID groups.

Addresses in VUS can be dynamically mapped into addresses in VDS with the help of the allocation module 105 operable to provide translation from VUA to VDA via Virtual Address Mapping.

By way of non-limiting example, FIG. 2 illustrates a part of the storage control layer corresponding to two LUs illustrated as LUx (208) and LUy (209). The LUs are mapped into the VUS. In a typical case, initially the storage system assigns to a LU contiguous addresses (VUAs) in VUS. However, existing LUs can be enlarged, reduced or deleted, and some new ones can be defined during the lifetime of the system. Accordingly, the range of contiguous data blocks associated with the LU can correspond to non-contiguous data blocks assigned in the VUS. The parameters defining the request in terms of LUs are translated into parameters defining the request in the VUAs, and parameters defining the request in terms of VUAs are further translated into parameters defining the request in the VDS in terms of VDAs and further translated into physical storage addresses.

Translating addresses of data blocks in LUs into addresses (VUAs) in VUS can be provided independently from translating addresses (VDA) in VDS into the physical storage addresses. Such translation can be provided, by way of non-limiting examples, with the help of an independently managed VUS allocation table and a VDS allocation table handled in the allocation module 105 as further detailed in U.S. application Ser. No. 12/897,119. Different blocks in VUS can be associated with one and the same block in VDS. Optionally, allocation of physical storage space can be provided only responsive to destaging respective data from the cache memory to the disks (e.g. for snapshots, thin volumes, etc.).

By way of non-limiting example, the Virtual Address Mapping can be provided with the help of one or more mapping data structures, for example configured as mapping trees detailed in U.S. application Ser. No. 12/897,119.

A non-limiting example of the mapping structure is illustrated in FIG. 3. For purpose of illustration only, the following description is provided for mapping trie(s) configured to provide mapping between VUA and VDA addresses. It should be noted that mapping between addresses related to logical volumes (LBA, VUA) and addresses (VDA, DBA) related to the physical address space can comprise at least one of the following mapping options: mapping between LBA and DBA addresses; mapping between VUA and VDA addresses; mapping between LBA and VDA addresses; and mapping between VUA and DBA addresses. When in some following examples a VUA offset is denoted as LBA address, it should be interpreted as VUA address corresponding to respective LBA address. Those skilled in the art will further readily appreciate that the presently disclosed subject matter is not bound by mapping with the help of mapping trees and can be implemented, likewise, with the help of any other appropriate mapping structure (e.g. mapping tables with respective entries and references therebetween). The mapping tree can be configured as an ordered tree (trie) data structure comprising one or more leaves wherein a) a depth of a leaf in the tree represents a length of a contiguous range of addresses related to a given corresponding logical group; b) a given path followed from a tree root to the leaf indicates an offset of the respective range of addresses within the given logical group; c) a value associated with the leaf indicates an offset of respective contiguous range of addresses related to the physical storage space and corresponding to said contiguous range of addresses related to said given logical group.

The depth of a given leaf can be configured in inverse relation to the length of respective contiguous range of addresses related to a respective logical group. A sequential number of a given leaf node can be calculated as D-1, wherein D is equal to a maximal admissible number of addresses related to the physical storage space divided by a number of contiguous addresses in the range of addresses related to the logical group.

The path followed from a tree root to the leaf can be represented as a string of zeros and ones depending on right and/or left branches comprised in the path. The offset of the respective range of addresses within the given logical group can be calculated in accordance with the path followed from the tree root to the leaf with the help of the following expression:

$\sum\limits_{i = 0}^{d - 1}{r_{i} \cdot 2^{({M - i - 1})}}$

where M is the power of two in the maximal number of admissible addresses in the given logical group, d is the depth of the leaf, i=0, 1, 2, 3, d-1 are the successive nodes in the tree leading to the leaf, and r, is a value equal to zero for one-side branching and equal to one for another side branching.

The mapping tree can comprise at least one leaf with at least two associated values, said associated values indicating offsets of two different contiguous ranges of addresses related to the physical storage space and corresponding to the same contiguous range of addresses related to the logical address space.

As illustrated by way of non-limiting example in FIG. 3, successive addresses in VUA can be mapped in several groups of successive VDA addresses. A data portion 301 in VUA is mapped to four different portions of successive blocks (302-305) in VDS. Mapping between VUA and VDS addresses is provided with the help of mapping structure 306 configured, by the way of non-limiting example as a mapping trie. Each VDS successive block starts at the address specified in the respective leaf and has a length corresponding to the depth of the branch, as was detailed above.

Bearing the above in mind, attention is drawn to FIG. 4 illustrating a method of migrating at least one data portion from a source logical volume V_(src) to one or more destination logical volumes V_(dest) in accordance with certain embodiments of the presently disclosed subject matter.

Operations detailed with reference to FIGS. 4-7 can be provided with the help of the allocation module 105 or one or more modules in the control layer specially configured for the desired purposes (e.g. migration module, background module, etc.).

The data portion to be migrated (also referred to hereinafter as the source data portion) is characterized by length LGT_(x) and offset LBA_(x) in a source logical volume V_(src) and offset LBA_(y) in the destination volume V_(dest). For purpose of illustration only, it is assumed that the migrated data portion is an extent of file F. The file F is owned by a filesystem FS_(dest), associated with a logical volume V_(src). File F is to be migrated to a file system FS_(dest), associated with a logical volume V_(dest). If file F spans more than one extent of successive blocks within V_(src), the respective data portions (extents) can be migrated separately (e.g. one after the other) as part of an atomic operation of migrating the file. By way of non-limiting example, the migrated data portion can be an extent of a file F stored in volume V_(src) related to a file system FS1 associated with a virtual machine VM1, this file to be migrated to volume V_(dest) related to a file system FS2 associated with VM2 running on the same host.

Those skilled in the art will readily appreciate that the presently disclosed subject matter is not bound by migration of file extents and/or migration in virtual machine environment, and can be implemented, likewise, for migration of data portions and groups thereof belonging to any logical objects from a source logical volume to a destination logical volume.

Thus, a migration operation comprises migrating a data portion having length LGT_(x) and starting at a logical block address LBA_(x) in volume V_(src) to logical block address LBA_(y) in volume V_(dest). The migration of data portion can be described by a migration function MIGRT(V_(dest), LBA_(y), V_(src), LBA_(x), LGT_(x)). The range in the destination volume with offset LBA_(y) and length LGT_(x) is referred to hereinafter as a destination range.

In conventional art, migration of data portions between logical volumes can be provided with the help of the host (e.g. application running therein) which can read the respective data from the volume V_(src) and write it into volume V_(dest). Alternatively, as known in the conventional art, the migration can be performed by physical copying data from the location currently allocated to V_(src) to location corresponding to V_(dest), and redefining the meta-data accordingly, such copying provided without a host involvement.

The technique provided in accordance with certain embodiments of the currently presented subject matter, enables virtual copying of the source data portion from logical volume V_(src) to logical volume V_(dest) with neither need in physical copying any data nor need in host involvement in the migration process. The virtual copying can be provided with or without keeping the source instance of the data portion.

In accordance with certain embodiments of the presently disclosed subject matter, the storage control layer is configured (401) to comprise a source mapping data structure DS_(src) assigned to the source logical volume V_(src). The source mapping data structure is configured to map between one or more contiguous ranges of addresses related to the source logical volume and one or more contiguous ranges of addresses related to corresponding physical address space. The source data structure comprises at least one entry corresponding to a source logical address range associated with data portions (extents) to be migrated and indicative of respective ranges of addresses related to the physical address space and corresponding to the data portions. By way of non-limiting example, the source mapping data structure can be configured as an ordered tree TR_(src) comprising one or more leaves (entries) corresponding to the data portion to be migrated. The values associated with these leaves indicate respective ranges of addresses related to the physical address space and corresponding to the data portion to be migrated.

The storage control layer is further configured (402) to comprise a destination mapping data structure DS_(dest) assigned, respectively, to the destination volume V_(dest). The destination mapping data structure is configured to map between one or more contiguous ranges of addresses related to the destination logical volume and one or more contiguous ranges of addresses related to the corresponding physical address space.

Responsive to a migration command, the destination mapping data structure DS_(dest) is configured (403) to comprise an entry that includes a destination logical address range associated with the migrated data portion and a reference to the source data structure, wherein the reference comprises an indication of the source logical address associated with the source data portion in the source logical volume V_(scr) before migration. Thus a request related to the migrated data portion in the destination volume will be addressed (404) by the destination mapping data structure DS_(dest) to the respective entry in the source mapping data structure DS_(src) capable of further translating the request into addresses related to physical address space. Upon receiving an I/O request addressed to the migrated data portion in the destination volume V_(dsts), the destination mapping data structure DS_(dest) is looked up by the destination logical address to retrieve a reference to the source data structure indicative of the source logical address. In the source mapping data structure DS_(src), the source logical address associated with the source data portion is further looked up to retrieve the actual physical address. Thus, the source data portion is virtually copied to the destination logical volume.

The destination mapping data structure can be configured as an ordered tree TR_(dest) configured to map between one or more contiguous ranges of addresses related to the destination logical volume and one or more contiguous ranges of addresses related to corresponding physical address space. Responsive to a migration command, the destination mapping tree TR_(dest) is configured to include a leaf corresponding to the migrated data portion, wherein a value associated with said leaf indicates the source logical volume V_(scr) and the offset of the data portion therein before migrating. Thus, a request related to the migrated data portion and received by a destination mapping tree TR_(dest) will be addressed to the source mapping tree TR_(src) according to the value associated with the leaf. The source mapping tree will provide further translating the request into addresses related to physical address space.

Likewise, if the source data portion needs to be migrated to several destination volumes, the operations above are provided for each destination volume and associated data structures. Optionally, migration to multiple destination volumes can be provided as a single atomic operation.

It shall be noted that the disclosed operation of migrating a data portion between logical volumes can be considered as a virtual migration as it does not alter addresses corresponding to the data portion and related to the physical address space.

FIG. 5 schematically illustrates an exemplary mapping of addresses related to source and destination logical volumes into addresses related to physical storage space, and further details the migration operation detailed with reference to FIG. 4.

The source logical volume V_(s), (501) is provided with assigned mapping tree TR_(src) (503) configured to map, at least, between contiguous ranges of addresses related to the data portion 505 in the source logical volume and ranges of addresses related to corresponding physical address space. The data portion 505 is characterized by offset LBA_(x) and length LGT_(x). The exemplified mapping tree TR_(src) comprises four leaves, the values associated with these leaves indicate respective ranges of addresses related to the physical address space and corresponding to the data portion.

The destination logical volume V_(dest) (502) is provided with assigned mapping tree TR_(dest) (504) configured to map, at least between contiguous ranges of addresses related to the data portion 506 in the destination logical volume and ranges of addresses related to corresponding physical address space. The data portion 506 is the data portion 505 upon migration to the destination logical volume. The data portion 506 is characterized by offset LBA_(y) and length LGT_(x).

Responsive to a migration command MIGRT (V_(dest), LBA_(y), V_(src), LBA_(x), LGT_(x)) the destination mapping tree TR_(dest) is configured to include a leaf 507. This leaf corresponds to the migrated data portion with the offset LBA_(y) and the length LGT_(x), and the value associated with said leaf indicates the source logical volume V_(scr) and the offset LBA_(x) of the data portion 505 before migrating.

Optionally, the migrated data portion can replace data comprised in the destination volume prior to receiving the migration command MIGRT (V_(dest), LBA_(y), V_(src), LBA_(x), LGT_(x)) and mapped by the destination mapping tree TR_(dest) accordingly. In this case, upon receiving the migration command, the mapping tree is reconfigured so that the leaf 507 replaces any other leaves related to the data range characterizing the migrated data portion with the offset LBA_(y) and the length LGT_(x).

A read request READ (V_(dest), LBA_(y)+K, P) addressed to a data range with length P and offset K within the migrated data portion 506, will be served with the help of the destination mapping tree 504. The reference in the leaf 507 addresses to the source mapping tree TR_(src) for further translation. The source mapping tree TR_(src) will provide addresses related to physical address space and corresponding to data range LBA_(x)+K, P in the data potion 505 before migration to destination logical volume.

Thus, the data portion 505 has been virtually migrated from the source logical volume to the destination logical volume in a single, atomic operation, by means of a mere manipulation of metadata and without physical copying of data in the storage system.

Those skilled in the art will readily appreciate that, likewise, the disclosed process can be implemented upon receiving a merge request MERGE (Vdest, LBAy, Vsrc, LBAx, LGTx) if Vdest already contain data in the destination range when the data migration operation is initiated.

Mapping between addresses in a destination logical volume and addresses related to physical address space with the help of referenced data structure assigned to a source logical volume is referred to hereinafter as indirect mapping. A process of serving a request with the help of indirect mapping is referred to hereinafter as indirect addressing.

It shall be noted that in accordance with certain embodiments of the presently disclosed subject matter, a move command can be provided in a manner similar to the described above with regard to the migration command. Responsive to a move command MOVE (V_(dest), LBA_(y), V_(src), LBA_(x), LGT_(x)), there is provided an atomic operation comprising indirect mapping the migrated data portion to the addresses related to physical address space with the help of at least one entry associated with the source data portion in the source mapping data structure, and configuring this entry in the source data structure DS_(src) to bear a special mark indicative that the entry (e.g. the leaf in the mapping tree) is unavailable to a client.

Referring to FIG. 6, there is illustrated a generalized flow diagram of handling write requests addressed to the source data portion in the source volume.

In certain embodiments, there can be a need to keep and independently update the source data portion along with the migrated data portion.

In accordance with certain embodiments of the presently disclosed subject matter, the mapping data structures in the source and in the destination volumes are further configured (601) to bear an indication of a number of mapping trees indirectly mapping a given data portion in different logical volumes to the same contiguous range of addresses related to physical address space. This indication, indicative for a given extent of the number of separate instances of the extent indirectly mapped to the addresses related to physical address space corresponding to the extent is referred to hereinafter as multiple reference indication (MRI). The indication can be provided with the help of a reference counter associated with the source volume and one or more destination volumes and/or data portions in the volumes. The reference counter can be implemented as a separate data structure or, fully or partly, integrated with respective mapping data structures. By way of non-limiting example, the MRI value can be assigned to each leaf corresponding to the given extent in source and destination mapping trees, and be updated upon extent modification(s).

For a given extent, the reference counter is indicative of, at least, all leaves in the source tree bearing indication that there is at least one destination tree TR_(dest) mapping respective data portions to the same contiguous range of addresses related to physical address space. The reference counter can further comprise a data structure (e.g. a table) having entries corresponding to the extents and indicative of the MRI value. For example, the entry can contain the following fields for a given extent migrated to three destination volumes:

-   -   V_(src); LBA_(x); Length (in blocks or in sections); MRI=3;         V_(dest1), LBA_(y1); V_(dest2), LBA_(y2); _(Vdest 3), LBA_(y3);         etc.

When a given extent is migrated to a first destination volume, a corresponding entry is added to the table with the MRI=1 in MRI value field. Every time the given extent is migrated, the MRI value in the corresponding entry in the table is updated to indicate the amount of indirectly mapped separate instances of the given extent. Optionally, the reference counter table can include only entries with non-zero MRI value. As will be further detailed with reference to FIGS. 6-7, the MRI value is decreased responsive to modification of one of the instances. When MRI value reaches zero, the respective entry can be deleted from the table.

For purpose of illustration only, the following description is provided for write requests addressed to the address range in the source volume corresponding to the entire extent migrated to a single destination volume. Those skilled in the art will readily appreciate that the presently disclosed subject matter can be implemented, likewise, when there are several instances of the extent migrated to several destination volumes.

Upon receiving by the source volume a write request WRITE (V_(src), LBA_(x), LGT_(x)), the following steps 602-607 are provided as a single atomic operation, i.e. operation that either succeeds or fails in its entirety and not in a partial way. The atomic operation comprises:

-   -   assigning a new contiguous range of addresses related to         physical address space for the new data to be destaged (602) and         associating the range of physical addresses to the corresponding         virtual address range in the source mapping data structure;     -   decreasing MRI value in the reference counter table entry         corresponding to the extent (V_(src), LBA_(x), LGT_(x)) from one         to zero (and, optionally, removing the entry as MRI=0) (603);     -   changing the value of the leaf corresponding to the migrated         extent in the destination mapping tree TR_(dest) by replacing         the reference to the source volume with the physical address         range corresponding to the extent in the source mapping tree         TR_(src) (604);     -   decreasing MRI value in the leaf corresponding to the extent in         the destination mapping tree TR_(dest) from one to zero (605);     -   changing the value of the leaf corresponding to the migrated         extent in the source mapping tree TR_(srct) by replacing the         physical address range with the new physical address range         assigned at step 602 (606);     -   decreasing MRI value in the leaf corresponding to the extent in         the source mapping tree TR_(src) from one to zero (607).

In the illustrated case of a single destination volume, upon completing the atomic operation, the indirect mapping has been removed and each mapping tree points to respective different physical address ranges.

Those skilled in the art will readily appreciate that, likewise, the disclosed process can be implemented upon receiving a delete request DELETE (V_(src), LBA_(x), LGT_(x)) for deleting the extent from the source volume V_(src) after migration. Steps 602, 606 and 607 can be replaced by deleting the respective leaf in the source mapping tree TR_(srct).

In a case of several instances of the extent migrated to several destination volumes, additional care can be taken, upon overwriting the migrated extent in the source volume, for keeping the value of the offset related to the physical address space corresponding to the extent before migration, as well as for keeping the related metadata. By way of non-limiting example, step 604 can be modified so that the destination mapping tree TR_(dest) in a first destination volume V_(dest) is configured to point to the physical address range copied from the TR_(src). Leaves corresponding to other instances of the migrated extent shall be re-configured to refer to the first destination volume V_(dest) instead of the source volume V_(src), and MRI values updated accordingly. The entry corresponding to the extent can be removed from the reference counter table only when MRI becomes equal to zero. By way of alternative non-limiting example, the respective leaf in the source tree can bear the value of the old offset in addition to the value of the updated offset. In this case the old value is marked to be used only for indirect mapping for responses received from the destination volume(s). The old value can be deleted only when the value of respective MRI becomes equal to zero.

A write request addressed to the instance in the destination volume WRITE (Vdest, LBA_(y), LGT_(x)) replaces the reference to DS_(src) in the destination mapping structure DS_(dest) by the destination physical address allocated for new/overwriting data and reduces respective MRI value in the reference counter.

FIGS. 7 a and 7 b schematically illustrate the process detailed with reference to FIG. 6.

FIG. 7 a schematically illustrates the non-limiting example in which the VUA extent 705 in the source volume 701 has the migrated instance 706 in the destination volume 702. The source mapping tree TR_(src) (703) maps between contiguous range of VUA addresses corresponding to (LBA_(x), LGT_(x)) and VDA addresses related to the extent 705. The exemplified mapping tree TR_(src) comprises a single leaf 707 indicative of VDA_(x) of range of VDA addresses corresponding to the extent.

The destination mapping tree TR_(dest) (704) maps between VUA and VDA addresses related to the migrated extent 706. The exemplified mapping tree TR_(src) comprises a single leaf 708, while the value associated with said leaf indicates the source logical volume V_(scr) and the offset LBA_(x) of the extent 705.

Both leaves 707 and 708 bear MRI value MRI=1, indicating that there is one mapping tree indirectly mapping the instances of the extent to the same contiguous range of VDA addresses.

FIG. 7 b schematically illustrates the mapping trees illustrated in FIG. 7 a and is further modified in response to the write request WRITE (V_(src), LBA_(x), LGT_(x)). Leaf 707 has the new value and points to the new offset VDA_(xX) of the new contiguous (with length LGT_(x)) range of VDA assigned for new data to be destaged. Leaf 708 has the value VDA_(x) corresponding to the VDA offset of the extent in the source mapping tree TR_(src) before modification by the write request.

Both leaves 707 and 708 bear MRI value reduced to zero, indicating that there are no mapping trees indirectly mapping the instances of the extent to the same contiguous range of VDA addresses.

Referring now to FIG. 7 c, there is schematically illustrated a modification of the process detailed with reference to FIG. 6 for a case of a write request addressed to a part of the migrated address range in the source volume.

Upon receiving a write request WRITE(V_(src), LBA_(x)+K, P) addressed to the range 715 with offset from LBA_(x)+K and length=P, the source mapping tree 703 illustrated with reference to FIG. 7 a is modified at step 604 to comprise three leaves representing mapping of three different parts of the extent:

-   -   leaf 716 corresponding to the address range from LBA_(x) to         LBA_(x)+K;     -   leaf 717 corresponding to the requested address range from         LBA_(x)+K to LBA_(x)+K+P); and     -   leaf 718 corresponding to the address range from LBA_(x)+K+P to         LBA_(x)+LGT_(x));

Leaves 716 and 718 have VDA values corresponding to VDA addresses VDA₁ and VDA₃ originally mapped to the respective ranges. Value in the leaf 717 has the new value VDA₂₂ (instead of originally mapped value VDA₂) corresponding to the new location assigned to the requested range in the destage process.

Likewise, the destination mapping tree 704 illustrated with reference to FIG. 7 a is modified at step 606 to comprise three leaves representing mapping of three different parts of the migrated extent:

-   -   leaf 726 corresponding to the address range from LBA_(y) to         LBA_(y)+K;     -   leaf 727 corresponding to the requested address range from         LBA_(y)+K to LBA_(y)+K+P); and     -   leaf 728 corresponding to the address range from LBA_(y)+K+P to         LBA_(y)+LGT_(x));

Leaves 726 and 728 bear referencing to addresses in the source volume corresponding to addresses VDA₁ and VDA₃ originally indirectly mapped to the respective ranges. Leaf 727 has the value VDA_(x) corresponding to the VDA offset of the requested range in the source mapping tree TR_(src) before modification by the write request.

The reference counter table treats each of the leaves as a separate entry replacing entries corresponding to the extents 705 and 706 before the write request. Likewise, the MRI values are treated separately for each leaf. Leaves 716, 718, 726 and 726 bear MRI value MRI=1, while MRI value of leaves 717 and 727 is reduced to zero.

It is to be understood that the presently disclosed subject matter is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The presently disclosed subject matter is capable of other embodiments and of being practiced and carried out in various ways. Hence, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the presently disclosed subject matter.

It will also be understood that the system according to the presently disclosed subject matter can be implemented, at least partly, as a suitably programmed computer. Likewise, the presently disclosed subject matter contemplates a computer program being readable by a computer for executing the disclosed method. The presently disclosed subject matter further contemplates a machine-readable memory tangibly embodying a program of instructions executable by the machine for executing the disclosed method.

Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the presently disclosed subject matter as hereinbefore described without departing from its scope, defined in and by the appended claims. 

1. For use in conjunction with a storage system, a method of migrating at least one source data portion from a source logical volume V_(src) to at least one destination range in at least one destination logical volume V_(dest) thereby giving rise to at least one migrated data portion in said at least one destination logical volume V_(dest), the method comprising: configuring a source mapping data structure DS_(src) to comprise at least one entry associated with said at least one source data portion and indicative of mapping between one or more contiguous ranges of addresses corresponding to said at least one source data portion in the source logical volume V_(src) and one or more ranges of addresses corresponding to said at least one source data portion and related to a physical address space; and responsive to a migration command, configuring a destination mapping data structure DS_(dest) to comprise at least one entry associated with said at least one destination range and comprising a reference to said at least one entry in the source mapping data structure DS_(src), said at least one entry in the source mapping data structure DS_(src) to be used for mapping to addresses related to physical address space and corresponding to the source data portion and to the migrated data portion.
 2. The method of claim 1 further comprising addressing a request related to said migrated data portion received by said destination mapping data structure DS_(dest) to said at least one entry in the source mapping data structure DS_(src).
 3. The method of claim 1 wherein the destination mapping structure DS_(dest) is configured as a destination ordered mapping tree TR_(dest), and wherein said at least one entry in the destination mapping structure DS_(dest) is implemented as a leaf of said destination mapping tree TR_(dest), said leaf bearing, upon receiving the migration command, a reference to said at least one entry associated with said source data portion in the source mapping structure DS_(src).
 4. The method of claim 1 wherein the logical volumes V_(src) and V_(dest) are associated with different virtual machines.
 5. The method of claim 1 further comprising associating said at least one source data portion with a multiple-reference indication indicative of a number of migrated data portions in one or more destination volumes, said migrated data portions mapped to the addresses related to physical address space with the help of said at least one entry associated with the source data portion in the source mapping data structure.
 6. The method of claim 5 wherein said indication is provided with the help of a reference counter associated with the source mapping data structure DS_(src) and with the destination mapping structure DS_(dest).
 7. The method of claim 3 wherein the source mapping structure DS_(src) is configured as a source ordered mapping tree TR_(src), and wherein said at least one entry in the source mapping structure DS_(src) is implemented as a leaf of the tree TR_(src), the method further comprising associating said leaves in the source and the destination mapping trees with a multiple-reference indication indicative of a number of migrated data portions in one or more destination volumes, said portions mapped to the addresses related to physical address space with the help of said leaves.
 8. The method of claim 5 further comprising: responsive to a write request related to said at least one source data portion, providing an atomic operation, said atomic operation comprising: assigning a new range of addresses related to physical address space for new data to be destaged; updating said at least one entry in the source mapping structure DS_(src) to map between one or more contiguous ranges of addresses corresponding to said at least one source data portion in the source logical volume V_(src) and said new range of addresses related to physical address space; and updating said at least one entry in the destination mapping structure DS_(dest) to map between said at least one destination address range and addresses related to physical address space and referred to, before updating, via said at least one entry in the source data structure DS_(src), wherein, upon updating, said mapping is provided without referencing to the source mapping structure.
 9. The method of claim 8 further comprising updating the value of multiple-reference indication associated with said at least one source data portion and with said at least one migrated data portion.
 10. The method of claim 5 further comprising: responsive to a request to delete said at least one source data portion, providing an atomic operation, said atomic operation comprising: deleting said at least one entry in the source mapping structure DS_(src); updating said at least one entry in the destination mapping structure DS_(dest) to map between said at least one destination address range and addresses related to physical address space and referred to, before updating, via said at least one entry in the source data structure DS_(src), wherein, upon updating, said mapping is provided without referencing to the source mapping structure; and updating the value of multiple-reference indication associated with said at least one migrated data portion.
 11. The method of claim 5 further comprising: responsive to a write request related to said at least one migrated data portion, providing an atomic operation, said atomic operation comprising: assigning a new range of addresses related to physical address space for new data to be destaged; updating said at least one entry in the destination mapping structure DS_(destt) to map between said at least one destination address range and said new addresses related to physical address space and corresponding to the migrated data portion, wherein said mapping is provided without referencing to the source mapping structure; and reducing by one the value of multiple-reference indication associated with said at least one source data portion.
 12. The method of claim 1, wherein migration operations for a plurality of source data portions constituting a logical object are provided as a single atomic operation.
 13. The method of claim 1 wherein said migrating does not alter addresses related to the physical address space and corresponding to said at least one source data portion and said at least one migrated data portion.
 14. A storage system comprising a plurality of physical storage devices constituting a physical storage space and controlled by a plurality of storage control devices constituting a storage control layer, wherein the storage control layer is operable to enable migrating at least one source data portion from a source logical volume V_(src) to at least one destination range in at least one destination logical volume V_(dest) thereby giving rise to at least one migrated data portion in said at least one destination logical volume V_(dest), the storage control layer further comprising: a source mapping data structure DS_(src) configured to comprise at least one entry associated with said at least one source data portion and indicative of mapping between one or more contiguous ranges of addresses corresponding to said at least one source data portion in the source logical volume V_(src) and one or more ranges of addresses corresponding to said at least one source data portion and related to a physical address space; and a destination mapping data structure DS_(dest) configured to comprise at least one entry associated with said at least one destination range and indicative of mapping between said at least one destination range and one or more ranges of corresponding addresses related to the physical address space; wherein said storage control layer is further operable to configure, responsive to a migration command, said at least one entry in the destination mapping data structure DS_(dest) to comprise a reference to said at least one entry in the source mapping data structure DS_(src), said at least one entry in the source mapping data structure DS_(src) is configured to be used for mapping to the addresses related to physical address space and corresponding to the migrated data portion and to the source data portion.
 15. The system of claim 14 wherein the destination mapping structure DS_(dest) is configured as a destination ordered mapping tree TR_(dest), and wherein said at least one entry in the destination mapping structure DS_(dest) is implemented as a leaf of said destination mapping tree TR_(dest), said leaf bearing, upon receiving the migration command, a reference to said at least one entry associated with said source data portion in the source mapping structure DS_(src).
 16. The system of claim 14 further comprising a plurality of virtual machines, wherein the logical volumes V_(src) and V_(dest) are associated with different virtual machines.
 17. The system of claim 14 wherein the storage control layer is further configured to provide associating said at least one source data portion and said at least one migrated data portion with a multiple-reference indication indicative of a number of migrated data portions in one or more destination volumes, said migrated data portions mapped to the addresses related to physical address space with the help of said at least one entry associated with the source data portion in the source mapping data structure.
 18. The system of claim 17 further comprising a reference counter associated with the source mapping data structure DS_(src) and with the destination mapping structure DS_(dest) and configured to provide said multiple-reference indication.
 19. The system of claim 15 wherein the source mapping structure DS_(src) is configured as a source ordered mapping tree TR_(src), and wherein said at least one entry in the source mapping structure DS_(src) is implemented as a leaf of the tree TR_(src), and wherein said leaves in the source and the destination mapping trees are associated with a multiple-reference indication indicative of a number of migrated data portions in one or more destination volumes, said portions mapped to the addresses related to physical address space with the help of said leaves.
 20. The system of claim 17, wherein the storage control layer is further configured to provide an atomic operation responsive to a write request related to said at least one source data portion, said atomic operation comprising: assigning a new range of addresses related to physical address space for new data to be destaged; updating said at least one entry in the source mapping structure DS_(src) to map between one or more contiguous ranges of addresses corresponding to said at least one source data portion in the source logical volume V_(src) and said new range of addresses related to physical address space; and updating said at least one entry in the destination mapping structure DS_(dest) to map between said at least one destination address range and addresses related to physical address space and referred to, before updating, via said at least one entry in the source data structure DS_(src), wherein, upon updating, said mapping is provided without referencing to the source mapping structure.
 21. The system of claim 17, wherein the storage control layer is further configured to provide an atomic operation responsive to a request to delete said at least one source data portion, said atomic operation comprising: deleting said at least one entry in the source mapping structure DS_(src); updating said at least one entry in the destination mapping structure DS_(dest) to map between said at least one destination address range and addresses related to physical address space and referred to, before updating, via said at least one entry in the source data structure DS_(src), wherein, upon updating, said mapping is provided without referencing to the source mapping structure; updating the value of multiple-reference indication associated with said at least one migrated data portion.
 22. The system of claim 17, wherein the storage control layer is further configured to provide an atomic operation responsive to a write request related to said at least one migrated data portion, said atomic operation comprising: assigning a new range of addresses related to physical address space for new data to be destaged; updating said at least one entry in the destination mapping structure DS_(dest) to map between said at least one destination address range and said new addresses related to physical address space and corresponding to the migrated data portion, wherein said mapping is provided without referencing to the source mapping structure; updating the value of multiple-reference indication associated with said at least one source data portion and with said at least one migrated data portion.
 23. A computer program product comprising a non-transitory computer useable medium having computer readable program code embodied therein for migrating, in conjunction with a storage system, at least one source data portion from a source logical volume V_(src) to at least one destination range in at least one destination logical volume V_(dest) thereby giving rise to at least one migrated data portion in said at least one destination logical volume V_(dest), the computer program product comprising: computer readable program code for causing the computer to configure a source mapping data structure DS_(src) to comprise at least one entry associated with said at least one source data portion and indicative of mapping between one or more contiguous ranges of addresses corresponding to said at least one source data portion in the source logical volume V_(src) and one or more ranges of addresses corresponding to said at least one source data portion and related to a physical address space; computer readable program code for causing the computer to configure a destination mapping data structure DS_(dest) to comprise at least one entry associated with said at least one destination range and indicative of mapping between said at least one destination range and one or more ranges of corresponding addresses related to the physical address space; computer readable program code for causing the computer to configure, responsive to a migration command, said at least one entry in the destination mapping data structure DS_(dest) to comprise a reference to said at least one entry in the source mapping data structure DS_(src), said at least one entry in the source mapping data structure DS_(src) to be used for mapping to the addresses related to physical address space and corresponding to the migrated data portion. 